BILLINGS, Mont. (AP) — Railroads that haul volatile crude shipments have reached an agreement with U.S. transportation officials to adopt wide-ranging, voluntary safety measures after a string of explosive and deadly accidents.

A copy of the agreement between the U.S. Transportation Department and the Association of American Railroads was obtained Friday by The Associated Press.

It calls for railroads to slow down oil trains through major cities, increase track inspections and bolster emergency response planning along routes that carry trains hauling up to 3 million gallons of oil each. Those trains travel thousands of miles from oil producing areas, including the Northern Plains, to coastal refineries.

The agreement does not resolve concerns over another fuel, ethanol, that's also seen a spate of accidents as production has increased. Railroads and federal officials said they would address separately a design flaw in tens of thousands of tank cars that make them prone to rupture during derailments.

(Reuters) - BNSF Railway Co plans to move into tank car ownership and buy its own fleet of up to 5,000 new crude oil tank cars with safety features that exceed the latest industry standards, the unit of investor Warren Buffett's Berkshire Hathaway Inc (BRKa.N) said on Thursday.

The unusual step by one of the largest U.S. railroads aims to reduce the risks of moving crude by rail after several recent accidents, including one involving a BNSF train in North Dakota in December.

The company, a major mover of crude by rail throughout the United States, plans to seek bids from railcar makers for up to 5,000 new tank cars with thicker walls and ends, increased protection of safety and pressure valves, and other features that go beyond industry standards adopted two years ago.